Stereo piezoelectric transducer



Feb. 1, 1966 P. WEATHERSL 3,233,047

STEREO PIEZOELECTRI C TRANSDUCER Filed Oct. 2, 1961 2 Sheets-Sheet 1 54ZAZB 82 w F INVEN TOR. ff 4 QA aL WfA THE/2s Feb. l, 1966 P. WEATHERS3,233,047

STEREO PIEZOELEGTRIC TRANSDUCER Filed Oct. 2. 1961 2 Sheets-Shea?l 2TRANsMswN FREQUENCY ne O5 no 52. f L-J 88 L om" qll-0 INVENTOR.

PAUL WEATHE/S United States 3,233,047 STEREO PIEZOELECTRTC TRANSDUCERPaul Weathers, Barrington, NJ., assignor to Teleprompter Corporation,New York, N.Y., a corporation of New York Fiied Oct. 2, 1961, Ser. No.142,145 2t) Claims. (Cl. 179-100.4)

The present invention relates to improved structures and arrangementsuseful in electromechanical transducers `and systems of the type inwhich mechanical motion is transduced into representative electricals-ignals.

More particularly, the present invention relates to improved structuresand arrangements useful in transducers of the type generally known aselectromechanical phonograph pick-ups and/ or systems, and especiallysuch pick-ups and systems as are intended for use in reproducingstereophonieally related sound signals as recorded on groovedstereophonic recordings. In such recordings, quadrature relatedundulations of the groove walls thereof represent records of twoseparate and distinct sound signals each corresponding to a differentone of a pair of signals making up stereophonic sound program material.

One of the more common approaches taken in providing a transducerstructure and system suitable for transducing mechanical motion intoelectrical signals, involves the use of 'a displacement sensit-iveelement which is, in turn, mechanically coupled to a sensing arm or beammember which in turn is directly subjected to the motion to betransduced. The displacement sensitive element may take a variety offorms such a variable capacitor, a variable inductance, a variableresistance, a moving coil in a magnetic field, a movable magneticallypermeable member forming part of a magnetic circuit, etc. In more recentyears, bodies of electrically piezosensitive or piezo electric materialhave been employed which exhibit one or more electrical characteristicswhich change upon the production of mechanical Kstress or strain thereinas by compressing, stretching, twisting or bending the body. Somepiezosensitive compositions reflect a change in resistance when sostressed. A quartz crystal, on the other hand, is known to generate anacross its faces upon producing strain therein. Similarly certainceramic dielectric materials such as barium titanate or leadzirconate-lead titanate compositions exhibit electrical dielectricproperties which change when bodies thereof are stressed. Such changesare in turn reflected in the development of an across surfaces of thebodies especially when the material has been electrically stressed orpolarized during manufacture. Such electrically piezosensitive orpiezoelectric vbodi `s are usually provided with conductive electrodeson two or more of their surfaces whereby changes in one or more of theirelectrical characteristics may be sensed during stressing of thematerial.

Generally speaking, most of the more common electrically piezosensitivematerials of the type described are quite stiff so that a substantialamount of work must be done in producing significant stresses therein.Because of this, the fabrication of a transduced based on their usebecomes challenging where little motional restraint can be tolerated onthe member whose motion is to be analyzed.

For example, a common form of transducer or pickup useful in reproducingor playing back present day grooved sound disc recordings comprises abody of electrically piezosensitive material carried by a supportstructure. This structure i-s adapted for fastening to a pickup arm. Abeam member is resiliently mounted to the support structure and providedat its free extremity with Patented Feb. l, 1966 a pointed stylus soshaped as to engage the v-shaped groove of a disc recording while thedisc is rotated on a turntable. Means are then provided in thetransducer for mechanically coupling the beam to the body ofpiezosensitive material. Motion of the stylus in tracing ,theundulations of the disc grooves is thereby communicated to thepiezosensitive body and the resulting changes in its electricalcharacteristic sensed and transformed into electrical signals.

ln high fidelity gr-ooved recordings, the undulations of the grooverepresenting high frequencies are quite abrupt. Hence, to minimize wearon the material from which the record is made, the effective moving massof the stylus should be as low as possible and the compliance of thebeam to which it is attached should be as high as possible. Furthermore,if the electrical signals ultimately produced are to faithfullyrepresent the recorded sound, the mechanical system comprising thestylus, beam and body of piezosensitive material should be free ofmechanical resonances within the range of sound frequencies recorded onthe disc. Thus, if the beam is directly coupled to the piezosensitivebody at or near the stylus extremity thereof, the stiffness of the bodyis directly imposed `on the stylus. Its effective mass is, therefore,high and it-s compliance low, resulting in undue record wear. On theother hand, if the mechanical coupling of the stylus to the body isreduced, as by resiliently mounting the body within the pick-up andcoupling the beam to the body at a position on the beam more remote fromthe stylus, various mechanical resonances are invited and the outputsignal from the pick-up is reduced.

Such resonances tend to distort the signal ultimately reproduced. Thistype of distortion is particularly troublesome in pick-ups intended forthe playback of present day stereophonic grooved recordings, for herethe undulations of the grooves have to be faithfully resolved into twoquadrature related vec-torial components. In such pick-ups, two bodiesof electrically piezosensitive material are employed and the motion ofthe beam coupled to these bodies in such a way that each body issubjected to stresses corresponding to a different one of thesevectorial components. Mechanical resonances and other nonlinearities inthe mechanical coupling of the beam to such bodies not `only producedistortion in the resulting signals, but tend to intercouple or mix thetwo stereophonic signals which are sought. This cross talk acts todestroy the stereophonic effect of the signals when audibly reproduced.Moreover, in stereophonic type pick-ups, yas well as standard monauralpick-ups, i-t is important that the effective degree of coupling of thebeam to each of the bodies remain substantially the same for allpositions of the stylus beam. Variations in such coupling tend toproduce asymmetries in response whereby undesirable in-termodulationdistortion occurs between low and high frequency signals. This effect ismainly attributable to the fact that in present day grooved soundrecordings, low frequency signals of a given energy level arerepresented by larger lgroove undulations than high frequency signals ofthe same energy level.

The present invention makes possible the realization of improvedtransducers and transducer systems of the type described which exhibithigh compliance, low mass, low distortion and a wide range frequencyresponse `and are characterized by high signal output and highdiscrimination in resolving the separate vectorial components of a givenmotion.

In accordance with one aspect of the present invention, high compliantbeam motion in an electrical piezosensitive transducer is realized byresiliently mounting the piezosensitive body to a support structurealong a substantial portion of but one of its surfaces. A beam is thenalso resiliently supported at one of its extremities to the supportstructure and also resiliently coupled to one extremity of theelectrically piezosensitive body at a position on the beam at or nearthat extremity thereof which is resiliently supported. A stylus adaptedto engage the grooves of a grooved disc sound recording is then fastenedto the other extremity of the beam. Ratios of 80' to 150 to 1 arethereby realized between stylus motion and the inotio-n imparted to thepiezosensitive body.

In further accordance with the invention, increased beam compliance insuch a transducer is realized by employing an electrical signalamplifier incorporating a substantial amount of degeneration at least inpart produced by the application of a negative feed back signal to thetransducer itself. By using a piezoelectric material having appropri atepolarization characteristics this same degenerative feed back signal ismade to produce a degree of positive electromechanical feed back whichaids stylus motion but is in degree less than the overall degenerationproduced in the amplifier.

In accordance with a further aspect of the present invention, increasedsignal output is realized by rigidly fastening that extremity of thepiezosensitive bo-dy most remote from the area thereof which is coupledto the beam to the support structure itself.

In accordance with still another aspect of the present invention,decreased intermodulation distortion between low and high frequencysignals delivered from transducers of the type described andspecifically employed for the playback of groot/ed phonograph discrecordings is realized by coupling the stylus carrying beam to aresiliently mounted body of piezosensitive material through a body ofresilient material having a tapered surface in direct contact with thebody of piezosensitive material.

In accordance with still another aspect of the invention, increasedsignal output realized from transducers ern ploying a polarizedpiezoelectric ceramic dielectric body as a stress sensitive element isincreased through the use of means applying a direct current biasvoltage across the body with such polarity that the instantaneousvariations in the voltage across the body attributable to capacitancechanges supplement and enforce voltages otherwise produced by variationsin the stress applied to the body.

In accordance with yet another aspect of the invention, cross talkbetween the two signals developed by a stereophonic phonograph pick-upemploying two bodies of piezosensitive material is reduced by arrangingthe major surface areas of the bodies to which pressure variations areapplied s that the surfaces lie in planes which intersect one another atan angle greater than 90 but less than 180.

The above as well as other novel features or advantages embraced by thepresent invention will be better understood through thefollowingspecification especially when read in connection with the accompanyingdrawings, in which:

FIG. 1 is a partially sectioned side view of a transducer embodyingfeatures of the present invention and particularly adapted for thereproduction of stereophonic sound recordings;

FIG. 2A is a sectional View of the structure shown in FIG. 1 taken alongthe arrowed lines ZA-ZA thereof looking in the direction of the arrows;

FIG. 2B is another sectional View of the structure shown in FIG. 1 takenalong the arrowed lines ZB-ZB looking in the directionof the arrows;

FIG. 3 is a rear end projection view of the structure shown in FIG. 1;

FIG. 4 is a bottom view of the structure shown in FlG. 1 with part ofthe outer casing of the transducer removed;

FIG. 5 is a graphical representation of the manner in which certaincharacteristics of the structure shown in FIG. 1 affect the overallfrequency response of the transducer; and

FIG. 6 is a schematic representation of a polarized held into position.

I :as shown at 32 and 34.

degenerative amplifier circuit suitable for use in connection with thetransducer structure shown in FIG. 1.

Turning now to FIGS. 1 through 4, one form of transduoer embodying novelfeatures in accordance with the present invention is illustrated. Theparticular form of transducer shown is one suited for use in thereproduction `or playback of grooved disc stereophonic recording of the45-45 type commonly in use today. The transducer comprises a supportmember 12 upon one surface of which four electrically conductivemetallic strips 14, 16, 1S and 20 have been placed and adhesively orotherwise firmly The supporting member 12 may be nothing more than athin sheet of electrical insulating material such as Bakelite or plasticwhile the conductive :strips may be made of phosphor bronze or springbrass. Extensions 14', 16', 18 and 20 of the metallic strips are bent(.as best shown in FIG. 1 and FIG. 4) and crimped around a body 22 ofinsulative elastic material, such as rubber, to form four electricalfemale contact terminals adapted for respective sliding contactengagement with `corresponding conductive strips held on the surface ofa detachable male plug 24. Only one of such latter strips is shown at25.

Also rigidly fastened to the supporting member 12 is a body of resilientmaterial 26 which, by way of example, is preferably made of eboniterubber having a durometer rating between 50 and 80. In the practice ofthe invention, ebonite rubber suitably loaded with frictionally lossymaterials (such as silicone) and cured by heating at a temperature of350 to 450 F. for a period of five to ten minutes is found to be verysatisfactory. The body 26 of resilient material is formed to have twosupporting surfaces 23 and 30. To each of these surfaces there is inturn fastened a body of electrically piezosensitive material In apreferred form of the invention, these bodies are comprised of a ceramiccompound made up of barium lead titanate-lead zirconate which is wellknown to have piezoelectric properties. Other materials havingelectrical characteristics which change with pressure may be used.Typically each of the bodies 32 and 34 'are approximately .250 inlength, .06" wide and .02" deep. Opposite major side surfaces of eachbody, to wit, surfaces 32a, 3217, 34a and 34h have ailixed thereto anelectrically conductive coating or elecytrode whereby changes in theelectrical characteristics of the material when placed under stress maybe sensed. Wires 36, 38, 40 and 42 conductively fastened to theseconductive coatings are in turn conductively aixed to a respectivelydifferent one of the metallic strips 14, 16, 18 and 20 whereby theelectrical characteristics of the electroded bodies 32 and 34 may beexternally sensed from connections (not shown) made to the male plug 24.

As indicated in the drawings, in a preferred form of the invention, theelectroded bodies 32 and .'54 are affixed to the resilient supportingbody 26 over a substantial portion of the area of their major sidesurfaces 32a and 34a. These areas are central to and between two smallerend areas of the major side surfaces 32a and 34a generally shown at 44and 46. In the particular arrangement shown, the lengths of the centralareas are approximately .15" each while the lengths of the end areas areapproximately .05 each. Another body 48 of resilient material, which maybe of the same character as the material forming body 26, is alsorigidly fastened to the supporting member 12 and is provided with anintegral extension generally rectangular in cross section shown at 50.The body :i8 is spaced away from the ends of the ceramic bodies 32 and34 by approximately .1 while the mean length of the extension 50 isapproximately .70. The rectangular cross section is approximately .06"square. Within a recess generally indicated by the dotted line 52, 'onelextremity of a tubular beam member S4 is rigidly fastened to theextension 50 as, for example, through the use of an adhesive or acement. The member 54 may be made of a lightweight aluminum tubing m25'long such as 24 ST available from the Precision Tube Company,

Philadelphia, Pennsylvania, the tube having a .029" diameter with a .002wall. The beam member 54 thus positioned extends generally along butaway from the major side surfaces 32b and 3417 of the ceramic bodies 32and 34 and through an opening generally shown at 56 in the lower portion58 of the transducer case. A stylus 60 shaped to engage the groove of adisc recording is cemented or otherwise held to the thus exposedextremity of the beam 54 within an aperture 62 therein. The resilientbody 43 which supports the beam 54 through the protrusion 50 is sopositioned relative to the end extremities 64 of the ceramic bodies 32and 34 that the tapered edge portions 66 and 68 of the rectangularextension S0 engage the end extremities 64 of the ceramic bodies 32 and34.

In a preferred form of the invention, the other end extremities of theceramic bodies 32 and 34 generally shown by the lines 74 are rigidlyfastened to the supporting structure 12 by means of a cement, wax, epoxyresin, etc. shown at 75. Where, in a preferred form of the invention,the ceramic bodies 32 and 34 are polarized, the bodies are positioned sothat the major side surfaces 3212 and 34h of the bodies exhibit the samepolarity of polarization relative to their opposing major side surfaces32a and 34a. This is generally indicated by the polarity signs in FIG.2B.

An upper portion 76 of the encasing structure is adapted for closesliding fit within the lower encasing structure 58 and is provided withwinged extensions $50 and S2 which are useful in supporting thetransducer in a phonograph pick-up arm (not shown) in accordance withwell known practice. The upper and lower portions of the transducerencasing structure are held together by means of crimping an extension59 of structure 5S over and around the end surface of structure 76.

In a preferred form of its utilization, the transducer shown in FIGS. lthrough 4 is employed in connection with two degenerative signalamplifiers each of which may take the form schematically illustrated inFIG. 6. As shown in FIG. 6, the eiectroded surfaces of either of theceramic bodies 32 and 34 are respectively applied to the input terminals86 and 88 of the amplifier arrangement. For purposes of illustrationonly, the ceramic body 32 is indicated as being connected to theamplifier, it being understood that the ceramic body 34 will beconnected to a similar circuit arrangement when using the transducer forreproduction of stereophonic records.

In FIG. 6, the input terminal S8 of the amplifier is connected to thebase of a transistor 90 which is connected as an emitter followeramplifier. This causes a relatively high impedance to appear between theinput terminals 86 and 88. For the purposes of the particular circuitshown, circuit ground terminal 92 is connected to the positive terminalof a source of operating potential (not shown). The negative terminal ofthis same source of operating potential is in turn connected to powersupply terminal 94. A resistor 91 is connected between the base oftransistor 90 and circuit ground. The emitter of transistor 90 is alsoconnected to ground through load resistor 96 while capacitor 98 couplessignals appearing across the resistor 96 to the base of the outputamplifier transistor 99. The emitter of the transistor 99 is in turnconnected to ground through a biasing resistor 100 which is in turnby-passed by capacitor 102. The collector of transistor 90 is directlyconnected to the negative power supply terminal 94 while the collectorof transistor 99 is connected through loading resistors 104 and 106 tothe negative power supply terminal 94. An output coupling capacitor 108is then connected from the collector of transistor 99 to an outputterminal 110. Signals appearing at the output terminal 110 are in turncoupled through capacitor 112 to terminal 114 which is galvanicallyconnected to the junction of resistors 104 and 106.

Terminal 114 of the circuit arrangement shown in FIG.

6 is in turn directly connected to the other input terminal 86 of theamplifier. Loading capacitor 116 is connected directly across the inputterminals 86 and 8S. A frequency compensating network made up ofcapacitor 118 and resistor 120 is connected from the terminal 86 tocircuit ground. Proper operating bias voltage for the transistor 99 isobtained by means of a resistive voltage dividing network made up ofresistor 122 and resistor 124 which is connected' between the negativepower supply terminal 94 and circuit ground, the junction 126 betweenthe two resistors being connected to the base of the transistor 99.

In the operation of the arrangement shown in FIG. 6, it can be seen thatthe ceramic body 32 of the transducer shown in FIGS. 1 through 4 will besubjected to a polarizing potential substantially equal in magnitude tothe power supply potential applied to the amplifier itself. If, in thepractice of the present invention polarized ceramic elements are used,the polarization of the ceramic elements are so arranged that theportion of the output signal appearing at terminal 110 which is coupledback to input terminal 86 via capacitor 112 acts upon the body 32 toassist stylus motion. At the same time, the fed back voltage acts toelectrically degenerate the signal appearing at terminal 88 of theamplifier. By adjusting the values of resistors 104 and 106, the degreeof the positive electromechanical feed back can be established at alower magnitude than the magnitude of the degree of electricaldegeneration described. In a preferred form of the invention, thedegenerative negative electrical feed back is established atapproximately 6 db greater than the positive electromechanical feedback. This provides greatly increased signal output and at the same timemaintains overall system stability.

In a typical embodiment of the transducer structure, as shown in FIGS. lthrough 4, it can be seen that the beam 54 extends generally away fromthe major surfaces 32h and 34h of the ceramic bodies 32 and 34. Inaccordance with the present invention, it has been found that to causethe signals developed by the ceramic elements 32 and 34 to representtruly quadrature related components of the motion of the stylus 60, theangle of reference planes passing through the major side surfaces 32band 34b must be made greater than the 90. It is found that the greaterthe angle which the longitudinal axis of the beam S4 makes with thesurfaces 32h and 34]; the greater the angle must be between the abovereference planes. In the particular arrangement shown, this angle isapproximately 125.

Moreover, in connection with the transducer shown in FIGS. l through 4,assymmetrical distortion of signals produced as a function of beamdisplacement (as above described) is reduced by adjusting the pressureswhich the tapered surfaces 66 and 63 of the extension 50 exert againstthe major surfaces 32h and 34:5 of the ceramic bodies. In final assemblyof the transducer, the resilient member 48 is adjustably positioned (asby a needle placed through aperture S6 in the encasing structure 58) andultimately affixed to the inner surface of the encasing structure 58through the use of an adhesive or cement shown at 149 applied throughaperture 56'. By this adjustment, the area of contact between the edgesof the resilient extension 50 and the surfaces of the ceramic bodies 32and 34 can be adjusted and their compressional characteristics made tocomplement the compressional elastic characteristics of the resilientsupporting body 26. Thus, referring to FIG, 2B, as the stylus beam 54 ismoved toward the ceramic body 34, the increased area of contact betweenthe protrusion 50 and the surface 34B will compensate for the forcesacting upon the surface 34a owing to the compressional characteristicsof the resilient body 26.

Furthermore, in the practice of the present invention, it iscontemplated that the configuration of the tapered edge surfaces 66 and68 of the extension 50 be tailored (as through the use of emory paper)to eect an almost perfect balance between thetransmissivity-versus-frequency characteristics of the resilientmaterial making up the extension 50 and the composite effectivetransmissivityversus-frequency characteristics of the ceramic elementsas mounted on the resilient support body 26. More specifically, athigher frequencies, the silicone loaded material making up extension 50tends to increase its transmissivity (as generally indicated by curve110 in FIG. 5), thus increasing the effective coupling between the beam54 and the ceramic bodies 32 and 34. On the other hand, owing to thefact that each of these bodies is rigidly fastened along a substantialportion of one of their surfaces to the loaded resilient body 26, asmaller length of the body is effectively stressed at higherfrequencies. Thus, the fulcrum arm, about which the bodies are stressed,becomes smaller as frequency increases. This is generally shown by curve112 in FIG. 5. Hence, by properly tailoring the edge surfaces 66 and 68of the extension Sti, the effective volume of the material which couplesthe beam to the ceramic bodies can be controlled and a balance betweenthe above effects realized. lt will be understood that the curves ofFIG. 5 are only exemplary of general effects above discussed and are inno way intended to depict specific characteristics of any particularmaterial or combination of elements.

From the above, it will be clear that the novel features of the presentinvention, although described in connection with a stereophonic typephonograph pick-up transducer, are useful in other types ofelectromechanical transducers such as monaural phonograph pick-uptransducers or transducers intended for general use in mechanicalvibration studies.

Having thus described the invention, what is claimed is:

l. ln a transducer for transducing mechanical motion Aintorepresentative electrical signals, the combination of:

a support member; a body of strain responsive material exhibiting agiven electrical characteristic which changes upon the production ofmechanical strain therein, said body having a first and a second endextremity and a first and a second major side surface opposing oneanother, each major side surface being comprised of two end areas eachembracing a different one of said end extremities and a central areaintermediate said two end areas, said central area being substantiallylarger than either of said end areas; means resiliently afhxing saidbody within the central area of said first major side surface to saidsupport member; means substantially rigidly affixing said body withinthe first end area of said first major side surface to said supportmember; a beam member having a first and a second end extremities; meansresiliently and directly coupling said first beam extremity to both saidsupport member and a variable area of that end area of said second majorside surface which directly opposes the second end area of said firstmajor side surface; the area coupled varying with the movement of saidsecond beam extremity relative to said support member; and meanselectrically connected to said body for sensing changes in said givenelectrical characteristic in response to movement of said second beamextremity relative to said support member.

2. In a transducer for transducing mechanical motion lintorepresentative electrical signals, the combination of: a support member;a body of strain responsive material exhibiting a given electricalcharacteristic which changes upon the production of mechanical straintherein, said body having a first and a second end extremity and a firstand a second major side surface opposing one another, each major sidesurface being comprised of two end areas each embracing a different oneof said end extremities and a central area intermediate said two endareas, said central area being substantially larger than either of saidend areas; means resiliently afl'ixing said body within a portion ofsaid lfirst major side surface to said support member leaving one endarea thereof free from direct coupling to said support member; a body ofresilient material fixed to said support member adjacent said firstextremity of said body of strain responsive material; a beam memberhaving one extremity thereof fastened to said body of resilient materialand extending generally along said second major side surface; meansresiliently coupling said beam member to a variable area of that endarea of said second major side surface which opposes said free end areaof said first major side surface at substantially the position on saidbeam member Where said beam member is fastened to said body of resilientmaterial; the area coupled varying with the movement of said second beamextremity relative to said support member; and means electricallyconnected to said body for sensing said changes in said given electricalcharacteristic of said body upon the movement of said beam relative tosaid support member,

3. In a system for transducing mechanical motion into representativeelectrical signals: a support structure; a first and a second electricalconductor carried by said support structure in electrically insulatedrelationship to one another; a beam member having two extremities; meansfastened to said support structure and holding one of said beam memberextremities to permit resilient movement of said beam member relative tosaid support structure; an electrical signal amplifier having two inputterminals; degeneration means included in said amplifier for producing`a degree of electrical degeneration of signals conditionally appearingacross said amplifier input terminals, said degeneration means includingstructure for developing and applying a degenerative feed back signal toone of said input terminals; means connecting each of said first andsecond electrical conductors to a different one of said amplifier inputterminals; a body of piezoelectric material fastened to said supportstructure, a variable yarea of which is mechanically coupled to saidbeam member to cause force conditionally produced by movement of eithersaid body or said beam member to be intercoupled between said body andsaid be-am thereby varying the area of coupling between said body andsaid beam, said body having a first and a second electroded surfaces;means holding at least a portion of said body in mechanically coupledrelationship to both said support structure and said beam; and meanselectrically connecting each o-f said first and second conductors tothat respectively different one of said electroded surfaces whichproduces a degree of electromechanical regenerative action between saidbody and said beam in response to said degenerative feed back signalapplied to said one amplifier input terminal.

4. in a system for transducing mechanical motion into representativeelectrical signals: a support structure; a first and a second electricalconducto-r carried by said support structure in electrically insulatedrelationship to one another; a beam member having two extremities; meansIfastened to said support structure and holding one of said beam memberextremities to permit resilient movement of said beam member relative tosaid support structure; an electrical signal amplifier having two inputterminals; degeneration means included in said amplifier for producing adegree of electrical degeneration of signals conditionally appearingacross said amplifier input terminals, said degeneration means includingstructure for developing and applying a degenerative feed back signal toone of said input terminals; means connecting each of said first andsecond electrical conductors to a different one of said amplifier inputterminals; a body of piezoelectric dielectric material fastened to saidsupport structure, a variable area of which is mechanically coupled tosaid beam member to cause force conditionally produced by movement ofeither said body or said beam member to be intercoupled between saidbody and said beam thereby varying the `area of coupling between saidbody and :said beam, said body having a first and a second electrodedsurface between which has been established a given fixed dielectricpolarization; means holding at least a portion of said body inmechanically coupled relationship t-o both said support structure andsaid beam; and means electrically connecting each of said first andsecond conductors to that respectively different one of said electrodedsurfaces which produces a degree of electromechanical regenerative-action between said body and said beam in response to said degenerativefeed back signal applied to said one amplifier input terminal.

5. In a system for transducing mechanical motion into representativeelectrical signals: a support structure; a first and a second electricalconductor carried by said support structure in electrical-ly insulatedrela-tionship to one another; a beam member having two extremities;means fastened to said support structure and holding one of said beammember extremities to permit resilient movement of said beam memberrelative tosaid support structure; an electrical signal amplifier havingtwo input terminals; degeneration means included in sa-id amplifier forproducing a degree of electrical degeneration of signals conditionallyappearing across said amplifier input terminals, said degeneration meansincluding structure for developing and applying a degenerative feed backsignal to one orf said input terminals; means connecting each of saidiirst and second electrical conductors to a different one o-f saidamplifier input terminals; a body of piezoelectric dielectric materialfastened to said support structure, a variable area of which ismechanically coupled to said beam member to cause force conditionallyproduced by movement of either said body or said beam member to beintercoupied between said body and said beam thereby varying the area ofcoupling between said body and said beam, said body having a first and asecond electroded surface between which has been established a givenfixed polarization; means holding at least a 4portion of said body inmechanically coupled relationship to both said support structure andsaid beam; means electrically connecting each of said first and secondconductors to that respectively different one of said electrodedsurfaces which produces a degree o-f electromechanical regenerativeaction between said bod-y and said beam in response to said degenerativefeed back signal applied to said one amplifier input terminal; and meansincluded in said amplifier for establishing 4a direct current voltagebias between said amplifier input terminals.

6. In la system for transducing mechanical motion into representativeelectrical signals: a support structure; a first and a second electricalconductor carried by said support structure in insulated relationship toone another; a beam member having two extremities; means fastened tosaid support structure and holding one olf said beam member extremitiesto permit resi-lient movement of said beam member relative to.` saidsupport structure; an electrical signal amplifier having two inputterminals; means connecting each of said first and second electricalconductors to a different one of said amplifier input terminals; a bodyof piezoelectric material fastened to said .support structure, avariable area yof which is mechanically coupled to said beam member tocause force conditionally produced by movement of either said body orsaid beam member to be intercoupled between said body and said beamthereby varying the area of coupling between said body and said beam,said body having a first and a second electroded surface; means holding7at least a portion of said body in mechanically coupled relationship toboth said support structure and said beam; means electrically connectingeach of said first and second conductors t-o that respectively differentone of said electroded surfaces which produces a degree ofelectromechanical regenerative action between said body and said beam inresponse to said degenerative feed back signal applied to said oneamplifier input terminal; and means included in said amplifier forestablishing a direct current voltage bias between said amplifier inputterminals.

7. In a transducer for transducing mechanical motion into two electricalsignals representing quadrature related components of the mechanicalmotion: a support member; a first and a second body of strain responsivematerial exhibiting a given electrical characteristic which changes uponthe production of mechanical strain therein, each of 4said bodies havinga substantially planar niajor side surface; means resiliently mountingsaid first and said second bodies to said support member with said majorside surfaces thereof adjacent one another and falling in respectivereference planes intersecting one another at an angle greater than butless than 180; a beam member having two extremities; holding meansaffixed to said support member and holding said beam at one of itsextremities while permitting fiexible movement of said other beamextremity relative to said support member in response to the motion tobe transduced, said holdinv means orienting the longitudinal axis of asubstantial portion of said beam along a direction generally away fromthe major side surface of said first and second bodies; meansresiliently coupling said beam to both said major side surfaces; andmeans coupled to said first and second bodies for separately detectingchanges in said given electrical characteristic in order to permit thedevelopment of two distinct electrical signals in response to movementof said beam member.

8. Apparatus according to claim 7 wherein said means resilientlycoupling said bea-m to both said major side surfaces comprises a body ofebonite rubber having a durometer rating of 55 to 80 and which has beencured by heating at a temperature between 300 to 400 for a period of 5to l0 minutes.

9. In a transd-ucer for transducing mechanical motion into twoelectrical signals representing quadrature related components of themechanical motion: a support member; a first and a second bodies ofstrain responsive material exhibiting a given electrical characteristicwhich changes upon the production of mechanical strain therein, each ofsaid bodies having a substantially planar major side surface; meansresiliently mounting said first and said second bodies to said supportmember with said major side surfaces thereof adjacent one another andfalling in respective reference planes intersecting one another; a beammember having two extremities; holding means aiiixed to said supportmember and holding said beam at one of its extremities while permittingfiexible movement of said other beam extremity relative to said supportmember in response to the motion to be transduced; a body of resilientmaterial rigidly fastened to said beam and having two portions on itssurface each tapering to a relatively thn edge, each edge directlycontacting the major side surface of a different one of said bodies ofstrain responsive material; and means coupled to said first and secondbodies for separately detecting changes in said given electricalcharacteristic in order to permit the development of two distinctelectrical signals in response to movement of said beam member.

10. In a transducer for transducing mechanical motion into twoelectrical signals representing quadrature related components of themechanical motion: a support member; a first and a second body of strainresponsive material exhibiting a given electrical characteristic whichchanges upon the production of mechanical strain therein, each of saidbodies having a substantially planar major side surface; meansresiiiently mounting said first and said second bodies to said supportmember with said major side surfaces thereof adjacent one another andfalling in respective reference planes intersecting one another at anangle greater than 90 but less than 180; a beam member having twoextremities; holding means affixed to said support member and holdingsaid beam at one of its extremities while permitting flexible movementof said other beam extremity relative to said support member in responseto the motion to be transduced, said holding means orienting thelongitudinal axis of said beam along a direction generally away from themajor side surface of said first and second bodies; a body of resilientmaterial rigidly fastened to said beam and having two portions on itssurface each tapering to a relatively thin edge, each edge directlycontacting the major side surface of a different one of said bodies ofstrain responsive material; and means coupled to said rst and secondbodies for separately detecting changes in said given electricalcharacteristic in order to permit the development of two dfstinctelectrical signals in response to movement of said beam member.

1l. In a transducer for transducing mechanical motion into twoelectrical signals representing quadrature relate-d components of themechanical motion: a support member; a first and a second body of strainresponsive material exhibiting a given electrical characteristic whichchanges upon the production of mechanical strain therein, each of saidfirst and second bodies having a substantially planar major sidesurface; means resiliently holding said first and said second bodies tosaid support member with said major side surfaces thereof adjacent oneanother and the longitudlnal extremities of said surfaces substantiallymutually co-extensive but with said surfaces falling in respectivereference planes intersecting one another at an angle greater than 90but less than 180; a resilient body of material rigidly fastened to saidsupport member at a position immediately adjacent one set of saidco-extensive longitudinal extremities of the major 'side surfaces ofsaid first and second bodies, said resilient body having a substantiallyrectangular projection forming a part thereof with each of two adjacentcorner portions of said projection contacting a respectively differentone of said major sde surfaces; a beam member having one extremityrigidly fastened to said resilient body and extending generally alongbut away from said first and second major side surfaces and saidresilient body; and means connected to said rst and second bodies forsensing changes in said given electrical characteristic in response tostrains produced in said first and second bodies by forces developed bybeam motion as communicated through said resilient body.

12. In a transducer for transducing mechanical motion into correspondingelectrical signals, the combination of: a support structure; a body ofstrain responsive material having a given electrical characteristicwhich is subject to change upon the production of stress therein, saidbody having a substantially flat surface; means resiliently mountingsaid body to said support structure in an orientation exposing saidsurface; a beam member resiliently mounted to said support structureadjacent said surface of said body; a body of resilient material havinga portion thereof tapering to a relatively thin edge with said edgeinterposed between said beam member and said surface with the apex ofsaid edge directly contactingsaid surface; and means coupled to saidbody of strain responsive material to permit the sensing of changes insaid given electrical characteristic in response to the relative motionbetween said beam and said surface which produces a variation in thearea of contact between said edge and said surface.

13. In a transducer for transducing mechanical motion into correspondingelectrical signals, the combination of: a support structure; a body ofstrain responsive material having a given electrical characteristicwhich is subject to change upon the production of stress therein, saidbody having a substantially flat surface; means resiliently mountingsaid body to said support structure in an orientation exposing saidsurface; a beam member resiliently mounted to said support structure ata position closely spaced from one longitudinal extremity of said flatsurface and extending along a direction adjacent said surface of saidbody; a body of resilient material having a tapered portion forming anedge interposed between said bearn member and said surface with the apexof said edge directly contacting said surface substantiatly at said oneextremity thereof; and means coupled to said body of strain responsivematerial to permit the sensing of changes in said given electricalcharacteristic in responsive to the relative motion between said beamand said surface which produces a variation in the area of contactbetween said edge and said surface.

14. In a transducer for transducing mechanical motion into correspondingelectrical signals, the combination of: a support structure; a body ofstrain responsive material having a given electrical characteristicwhich is subject to change upon the production of stress therein, saidbody having a substantially flat surface; means resiliently mountingsaid body to said support structure in an orientation exposing saidsurface; a beam member resilientiy mounted to said support structure vatla position closely spaced from one longitudinal extremity of said fiatsurface and extending along a 'direction adjacent said surface of saidbody; abody of resilient material interposed between said beam memberand said flat surface, said body having a tapered portion defining asurface of minimum area said surface of minimum area directly contactingsaid dat surface whereby incremental changes in the position of saidbeam member relative to said body produces a change in the total surfacearea common to said body of resilient material and said body of strainresponsive material; and means coupled to said body of strain responsivematerial to permit the sensing of changes in said given electricalcharacteristic in response to relative motion between said beam and saidsurface.

l5. in a transducer for transducing mechanical motion into correspondingelectrical signals, the combination of a support structure; a body ofstrain responsive material having a given electrical characteristicwhich is subject to change upon the production of stress therein, saidbody having a substantially flat surface; means resiliently mountingsaid body to said support structure in an orientation exposing saidsurface; a beam member resiliently mounted to said support structure ofa position closely spaced from one longitudinal extremity of said flatsurface and extending along a direction adjacent said surface yof saidbody; a body of resilient material having a tapered portion forming anedge interposed between said beam member and Vsaid surface with the apexof said edge directly contacting said surface substantially at said oneextremity thereof; 'means rigidly afxing the other extremity of saidbody to said support structure; and means coupled to said body of strainresponsive material to permit the sensing of changes in said givenelectrical characteristic in response to the relative motion betweensaid beam and said surface which produces a variation in the area ofcontact between Vsaid edge and said surface.

16. In a transducer for transducing mechanical motion into correspondingelectrical signals, the combination of: a support structure; a body ofstrain responsive material having a given electrical characteristicwhich is subject to change upon the production of stress therein, saidbody having a substantially flat surface; means resiliently mountingsaid body to said support structure in an orientation exposing saidsurface; a body of resilient material rigidly fastened to said supportstructure at a position thereon closely spaced from one longitudinalextremity of said flat surface and having an extension thereon whichphysically contacts said surface; a beam member having one of itsextremities embedded in and supported by said extension and extendingtherefrom in a direction generally along and adjacent said surface ofsaid body; and means coupled to said body of strain responsive materialto permit the sensing of changes in said given electrical characteristicin response to the relative motion between said beam and said surfacewhich produces a variation in the area of contact between said edge andsaid surface.

17. In a phonograph pickup system for producing separate electricalsignals each representing a different one of the two separate soundrecordings defined by quadrature related undulations of the groove wallsin a grooved stereophonic recording: a support structure; a first and asecond plate-like bodies Q'f piezoelectric dielectric material,

each of said plates having two major side surfaces each holding aseparate conductive electrode and each plate bearing a preformeddielectric polarization between said major side surfaces thereof; meansresiliently supporting said bodies adjacent one another upon saidsupport structure with the longitudinally running edges thereofdisplaced from and substantially parallel to one another with the mostclosely adjacent major surfaces of said bodies falling in respectivereference planes which intersect one another at an angle greater than 90but less than 180, the longitudinal extremities of said surfaces beingsubstantially co-extensive and forming two pairs of co-extensivelongitudinal extremities; a beam member having two extremities; holdingmeans rigidly affixed to said support structure and holding said beam ata first one of its extremities while permitting flexible movement of theother beam extremity relative to said support structure and directingsaid beam in a direction generally away from but generally along saidmost closely adjacent major surfaces of said bodies; a groove engagingstylus rigidly fixed to said beam at a position thereon near the secondone of said beam extremities; and means resiliently coupling said beamto both of said most closely adjacent major surfaces of said bodieswithin respective areas thereof immediately adjacent those co-extensiveextremities of said bodies nearest said holding means.

18. Structure according to claim 17 wherein the orientation of saidbodies is such that the most closely adjacent major surfaces of saidplates correspond to the same polarity of dielectric polarization.

19. Structure according to claim 17 wherein said holding means comprisesa solid body of resilient material rigidly afiixed to said supportstructure at a position closely displaced from one pair of saidco-extensive longitudinal extremities of said bodies and wherein saidmeans resiliently coupling said beam to the major surfaces of saidbodies comprising an integral extension of said solid body the surfaceof which extension physically contacts both of said major surfaces.

20. A system according to claim 17 wherein there is 'additionallyprovided a first and a second electrical signal amplifier each amplifierhaving two signal input terminals and means for producing a fixed directcurrent bias voltage of given polarity between said input terminals, andelectrical connections between each of the two conductive electrodes ofsaid first body to a respectively different input termin-al of saidfirst amplifier in a given polarity sense and electrical connectionsbetween each of the two conductive electrodes of said second body to arespectively different input terminal of said second amplifier in saidsame given polarity sense.

References Cited by the Examiner UNITED STATES PATENTS 2,516,338 7/1950Olson 179-100.4 2,858,373 10/1958 Hollmann 179-1004 2,953,648 9/1960Dieter 179-100.41

FOREIGN PATENTS 672,236 5/ 1952 Great Britain.

IRVING L. SRAGOW, Primary Examiner.

BERNARD KONICK, Examiner.

1. IN A TRANSDUCER FOR TRANSDUCING MECHANICAL MOTION INTO REPRESENTATIVEELECTRICAL SIGNALS, THE COMBINATION OF: A SUPPORT MEMBER; A BODY OFSTRAIN RESPONSIVE MATERIAL EXHIBITING A GIVEN ELECTRICAL CHARACTERISTICWHICH CHANGES UPON THE PRODUCTION OF MECHANICAL STRAIN THEREIN, SAIDBODY HAVING FIRST AND A SECOND END EXTREMITY AND A FIRST AND A SECONDMAJOR SIDE SURFACE OPPOSING ONE ANOTHER, EACH MAJOR SIDE SURFACE BEINGCOMPRISED OF TWO ENDS AREAS EACH EMBRACING A DIFFERENT ONE OF SAID ENDEXTREMITIES AND A CENTRAL AREA INTERMEDIATE SAID TWO END AREAS, SAIDCENTRAL AREA BEING SUBSTANTIALLY LARGER THAN EITHER OF SAID END AREAS;MEANS RESILIENTLY AFFIXING SAID BODY WITHIN THE CENTRAL AREA OF SAIDFIRST MAJOR SIDE SURFACE TO SAID SUPPORT MEMBER; MEANS SUBSTANTIALLYRIGIDLY AFFIXING SAID BODY WITHIN THE FIRST END AREA OF SAID FIRST MAJORSIDE SURFACE TO SAID SUPPORT MEMBER; A BEAM MEMBER HAVING A FIRST ANDSECOND END EXTREMITIES; MEANS RESILIENTLY AND DIRECTLY COUPLING SAIDFIRST BEAM EXTREMITY TO BOTH SAID SUPPORT MEMBER AND A VARIABLE AREA OFTHAT END AREA OF SAID SECOND MAJOR SIDE SURFACE WHICH DIRECTLY OPPOSESTHE SECOND END AREA OF SAID FIRST MAJOR SIDE SURFACE; THE AREA COUPLEDVARYING WITH THE MOVEMENT OF SAID SECOND BEAM EXTREMITY RELATIVE TO SAIDSUPPORT MEMBER; AND MEANS ELECTRICALLY CONNECTED TO SAID BODY FORSENSING CHANGES IN SAID GIVEN ELECTRICAL CHARACTERISTIC IN RESPONSE TOMOVEMENT OF SAID SECOND BEAM EXTREMITY RELATIVE TO SAID SUPPORT MEMBER.